Anti-glaucoma drug-loaded contact lenses prepared using supercritical solvent impregnation

Post-processing drug impregnation of commercially available polymer-based devices is a recent and attractive approach for the development of multifunctional biomedical devices and implants, drug release systems and tissue scaffolds. Therapeutic ophthalmic articles, such as drug-loaded contact lenses, are already known to improve ocular bioavailability in the treatment of several eye diseases, namely glaucoma, as well as to minimize undesired systemic side-effects. In this work, commercial silicone-based hydrogel contact lenses (Balafilcon A) were impregnated with two anti-glaucoma drugs (acetazolamide and timolol maleate) using a discontinuous supercritical solvent impregnation (SSI) methodology. Pressure and temperature, as well as impregnation time and depressurization rate, were kept constant (17 MPa, 40 degrees C, 90 min, 0.06 MPa/min, respectively) in order to evaluate the effects of nature and concentration of cosolvents (ethanol and water at 5, 10 and 15% molar) on the impregnation efficiencies and the properties of the contact lenses. Glass-transition temperature (DSC), oxygen permeability, contact angle, apparent morphological changes (SEM) and in vitro drug release kinetics were studied in detail. Results demonstrated the feasibility of preparing acetazolamide and timolol maleate impregnated therapeutic Balafilcon A contact lenses using CO2+EtOH and CO2+H2O solvent mixtures. Valuable information about how the nature and the composition of the employed solvent mixtures influence drug loading, drug release profiles and contact lenses physical and thermomechanical properties was obtained.